0001578: Incorrect stress term in UcEqn in DPMFoam/MPPICFoam - OpenFOAM Issue Tracking

ID	Project	Category	View Status	Date Submitted	Last Update

0001578	OpenFOAM	Bug	public	2015-03-20 13:27	2016-05-20 09:51

Reporter	~~user1084~~	Assigned To	henry
Priority	normal	Severity	minor	Reproducibility	always
Status	closed	Resolution	suspended
Platform	GNU/Linux	OS	Ubuntu	OS Version	14.10

Summary	0001578: Incorrect stress term in UcEqn in DPMFoam/MPPICFoam
Description	Following the bug thread here: http://www.openfoam.org/mantisbt/view.php?id=1563 it was concluded (by henry) that we eventually use the second option in Leboreiro as found here in equation 2.63/2.64 (discretized to a per-particle case): http://gradworks.umi.com/33/03/3303878.html I've checked all the equations in OpenFOAM and indeed we do use equation 2.63/2.64, including for instance dividing the drag by an extra factor alpha. However as is seen in 2.63 the gas momentum equation should contain the divergence of total stress, which is P + \tau. In UcEqn.H the stress is however multiplied by alpha, so we have div(alpha*\tau). This is incorrect and should be just div(\tau) as seen in the paper. If this is not done there is no consistent way of coupling the common two approaches, equations 2.57/2.58. Also the equations 2.63/2.64 are, in the case of including alpha with \tau in the divergence term, inconsistent with the Jackson approach, also referred to in that thesis or found in table 3.1 in this thesis: http://repository.tudelft.nl/assets/uuid:919e2efa-5db2-40e6-9082-83b1416709a6/as_wachem_20000918.PDF . Another way of seeing this is that the UcEqn effectively contains no terms anymore with alpha when including the pressure gradient force via the momentum transfer term, as the total pressure gradient force defined by DUcDt cancels the alpha in front of the transient and divergence term in the UcEqn. Clearly in this case then the viscuous stress \tau should also not have an alpha (pressure and gravity already don't have any alpha included, which is correct in this approach). I realize the impact is most likely small and therefore not very noticeable, but I think consistency is important. Secondly I would like to add that in the previous bug thread it was shown that the equations are inconsistent when the pressure gradient force is not included for DPMFoam/MPPICFoam (again referring to the thesis above), so to avoid confusion it would be nice if this term could be added to the tutorial dictionaries. I have also outlined the issue in the attached report; section 1.1 and 1.2.
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Date Modified	Username	Field	Change
2015-03-20 13:27	~~user1084~~	New Issue
2015-03-20 13:27	~~user1084~~	File Added: MPPICFoam.pdf
2015-03-24 00:17	liuhuafei	Issue cloned: 0001595
2016-05-04 20:45	henry	Note Added: 0006229
2016-05-20 09:51	henry	Status	new => closed
2016-05-20 09:51	henry	Assigned To	=> henry
2016-05-20 09:51	henry	Resolution	open => suspended